1. Field of the Invention
The invention relates to a torque converter installed on a vehicle, and, more particularly, to a technique for supporting a stator of the torque converter.
2. Description of Related Art
A torque converter for multiplying torque generated by a power source and transmitting the torque to the next power transmission stage includes an impeller called “stator”. The stator is mounted on a rotary shaft via a one-way clutch, and is operable to direct flow of working oil from a turbine runner toward an inlet of a pump impeller.
FIG. 13 shows a torque converter 1000 including a conventional support device of a stator 2000. Referring to FIG. 13, an aluminum washer 650 holds or maintains the spacing between a one-way clutch outer race 350 and a one-way clutch inner race 750. The aluminum washer 650 bears a load applied to a thrust bearing 450, via a thrust bearing race 550. In this case, the aluminum washer 650 that receives the load is required to have a sufficiently large thickness as measured in the axial direction, to provide sufficiently high rigidity. In fabrication of the conventional support device, the aluminum washer 650 is attached to the one-way clutch, and the thrust bearing 450 is further disposed outside the aluminum washer 650, resulting in an increase in the axial length of the device.
In the stator support device constructed as described above, the lifetimes of the one-way clutch and the thrust bearing 450 are influenced by loads received in the axial direction and radial directions. The lifetime of the stator is also influenced by such loads. In order to maintain the life of the stator, therefore, it is necessary to appropriately bear or sustain the loads, restrict “deviation” of the mounting position of the stator relative to the rotation axis, and provide sufficient lubrication. In addition to these requirement associated with the life of the stator, a demand for a reduction in the axial dimension of the stator is increasing so as to make the torque converter small-sized.
Japanese Laid-open Patent Publication No. 2001-323985 discloses a stator device having a reduced axial length. The stator device includes an outer wheel fixed on the inner circumference of the stator, an inner wheel disposed coaxially with the outer wheel, an end bearing that keeps a clearance or spacing between the outer wheel and the inner wheel, and a thrust washer composed of a bimetallic material used for bearings. The thrust washer serves to restrict axial movements of a one-way coupling device, such as a one-way clutch.
In the stator device as described above, the clearance between the outer and inner wheels is maintained by the end bearing, and the axial movements of the one-way coupling device is restricted by the thrust washer. With this arrangement, the length of a portion that supports the stator can be reduced to be shorter than the axial length of a conventional aluminum bushing.
Laid-open Publication No. 7-16049 of Japanese Utility Model Application discloses a stator support structure of a torque converter having a reduction axial dimension. The stator support structure includes an outer race fixed to a stator carrier of a stator, an inner race disposed radially inwardly of the outer race, a one-way clutch that permits rotation of the outer race only in one direction, and a support member disposed at a side face of the one-way clutch that is closer to a pump impeller.
In the stator support structure as described above, the support member is disposed at the side face of the one-way clutch closer to the pump impeller so as to support the outer race, inner race, and the one-way clutch. By providing the support member, in place of an radially inward flange formed integrally with the stator carrier, the axial dimension of a mounting portion of the stator can be reduced.
In the stator device disclosed in JP-A-2001-323985, since the thrust bearing race needs to receive a load from the thrust bearing and transmit the load to the stator, the thrust bearing race is required to have sufficiently high rigidity, resulting in an increase in the axial length of the race. Also, oil grooves for lubrication are needed for preventing wear due to frictional contacts with the inner race.
In the stator support structure disclosed in JP-U-7-16049, the dimensional accuracy of the clearance between the inner race and the outer race of the one-way clutch is reduced due to the use of the support member, and therefore the lifetime of the one-way clutch is reduced. Also, lubricant paths leading to the interior of the torque converter cannot be surely provided in the presence of the support member.